Which one is equivalent what’s the work that goes with it? i’m very confused

0if x and y vary inversely and y=6 as x=7, what is the constant of variation?

If 30 lb of rice and 30 lb of potatoes cost ? $27.60? , and 20 lb of rice and 12 lb of potatoes cost ? $15.04? , how much will 10 lb of rice and 50 lb of potatoes? cost?

Mila's dog weighs 4 pounds more than 8 times the weight of keiko's dog. which expression could be used to fine te weight of mila's dog?